Patients have a blood sample drawn before and after each new PS-341 injection to measure the drug action in the blood and to see how strong and how long the effects on the blood last. They are seen in the clinic at least once a week for a history and physical examination. A blood sample is collected at each visit to look for toxic effects of PS-341. Near the end of treatment, the neurocardiovascular evaluation is repeated, and if the results are abnormal, it is repeated again 3 months after treatment is completed. X-rays or MRI scans are done 12 weeks after radiation therapy has ended and then every few months after that to determine the extent of disease. Patients whose tumor is accessible are asked to undergo a biopsy (removal of a small piece of tumor tissue) on the first and second day after receiving the first PS-341 dose to examine the effect of the drug on the tumor.